Semiconductor light emitting device and method of making the same

Abstract

The invention provides a semiconductor light emitting device and the method of making it. The semiconductor light emitting device, according to the invention, includes an undoped In x GA y Al 2 N film, as an Ohmic layer, formed between a top-most semiconductor material layer and a transparent conductive oxide layer. Since the undoped film as a tunneling layer is very thin (≦20 angstroms), the electric field across the tunneling layer, under forward bias, will make electron tunneling from valence band to conduction band, and return to the transparent conductive layer, A reasonably low and stable forward voltage of the semiconductor light emitting device according to the invention can be achieved.

1. A semiconductor light emitting device, comprising:
 a semiconductor substrate; 
 a multi-layer structure formed on the semiconductor substrate, the multi-layer structure comprising a light emitting region; 
 an undoped film of In x Ga y Al z N overlaying the multi-layer structure, wherein x+y+z=1, and 0≦x,y,z≦1; and 
 a layer, consisting of a transparent conductive oxide, overlaying the undoped film; 
 wherein an operating forward voltage of said semiconductor light emitting device is determined by the following formula: 
 
     
       
         
           
             
               
                 V 
                 t 
               
               = 
               
                 EXP 
                 ⁡ 
                 
                   ( 
                   
                     
                       
                         - 
                         4 
                       
                       ⁢ 
                       
                         
                           ( 
                           
                             2 
                             ⁢ 
                             
                               
                                 m 
                                 * 
                               
                               · 
                               
                                 E 
                                 g 
                                 3 
                               
                             
                           
                           ) 
                         
                         
                           3 
                           / 
                           2 
                         
                       
                     
                     
                       3 
                       ⁢ 
                       
                         e 
                         · 
                         
                           h 
                           _ 
                         
                         · 
                         E 
                       
                     
                   
                   ) 
                 
               
             
             , 
           
         
       
       m * is the effective electron or hole mass, E g  is the effective band-gap of the undoped film, e is an electron charge, {overscore (h)} is the Plank's constant, and E is the electric field across the undoped film. 
     
   
   
     2. The semiconductor light emitting device of  claim 1 , wherein the undoped film is formed by an epitaxial process, and a thickness of the undoped film is less than or equal to 20 Angstroms. 
   
   
     3. The semiconductor light emitting device of  claim 1 , wherein the operating forward voltage is less than or equal to 3.7 Volts. 
   
   
     4. The semiconductor light emitting device of  claim 1 , wherein the transparent conductive oxide is one selected from the group consisting of ITO, ZnO, InO and ZrO. 
   
   
     5. The semiconductor light emitting device of  claim 1 , wherein the light emitting region comprises one selected from the group consisting of a PN-junction, a double hetero-junction and a multiple quantum well. 
   
   
     6. The semiconductor light emitting device of  claim 1 , wherein the multi-layer structure comprises a layer contacting the undoped film and formed from a matertal selected from the group consisting of GaN, AIGaN, InGaN and InGaAIN.